The present invention relates to a method of cleaning a diffusion reactor and an improved diffusion reactor suitable for cleaning the same, and more particularly to a method of efficiently cleaning depositions on an inner wall or jigs of a reaction chamber of a diffusion reactor and a diffusion reactor having a cleaning mechanism.
A diffusion reactor has a reaction tube or a reaction chamber which is cylindrically shaped. A plurality of semiconductor wafers are placed in the reaction chamber. The reaction chamber is heated at a predetermined temperature and further predetermined gases such as phosphate, nitrogen and oxygen are supplied to the reaction chamber, so that an impurity such as phosphorus is diffused into the semiconductor wafers.
As the diffusion reactor is repeatedly used, a deposition such as an impurity containing oxide film, for example, a phosphorus containing oxide film is deposited on the inner wall of the reaction chamber or the jigs in the reaction chamber. As the reaction chamber is heated, not only the intended impurity such as phosphorus is diffused into the semiconductor wafers but also the excess impurity in the deposition is re-diffused to the semiconductor wafers, whereby the impurity concentration of the semiconductor wafers exceeds the intended value. In order to prevent this problem, it is necessary that the deposition deposited on the inner wall of the reaction chamber or the jigs in the reaction chamber is removed periodically.
Japanese laid-open patent publication No. 61-176113 discloses the conventional cleaning method for cleaning the deposition adhered on the inner wall of the reaction chamber of the diffusion reactor. A roof side of the reaction chamber is provided with an air-intake/discharge port. A bottom side of the reaction chamber is also provided with an injection port for injecting a cleaning chemical and also with a discharge port for discharging the used cleaning chemical. The cleaning chemical is injected into the reaction chamber for allowing the cleaning chemical to be used as an etchant for carrying out a wet etching process. It is necessary that the roof side and the side wall contact the cleaning chemical. Namely, it is necessary that the predetermined amount of the cleaning chemical is reserved in the reaction chamber until the cleaning to the roof side and the side wall is completed. As a result, the bottom side of the reaction chamber is necessarily contacts the cleaning chemical for a longer time than necessary for cleaning the bottom side. This means that the bottom side of the reaction chamber is subjected to the over-etching due to the excessively long contact time with the cleaning, chemical. The over-etching to the bottom side of the reaction chamber reduces the thickness of the bottom side of the reaction chamber compared to the roof side and the side wall of the reaction chamber. A difference in thickness between the bottom side portion of the reaction chamber and the remaining portions thereof causes a difference in heat conductivity of the reaction chamber between the bottom side portion and the remaining portions thereof. This makes it difficult to uniformly heat the reaction chamber, whereby the required uniform impurity diffusion is not realized.
Further, when the reaction chamber is cleaned, the bottom of the reaction chamber is kept horizontal. This makes it difficult to discharge the used cleaning chemical completely. A small amount of the used cleaning chemical is likely to remain on the bottom side of the reaction chamber, whereby the remaining cleaning chemical further over-etches the bottom portion of the reaction chamber.
Furthermore, it is necessary that the injection port for injecting the cleaning chemical and the discharge port for discharging the used cleaning chemical are provided on a circumferential portion of the reaction chamber to avoid an uniformly heated region of the reaction chamber heated by the heater. This means it necessary to elongate the reaction chamber in its axial direction, whereby the diffusion reactor is enlarged in size and the necessary amount of the heat given by the heater is also increased.
In the above circumstances, it had been required to develop a novel diffusion reactor and method of cleaning the same free from the above problem.
Accordingly, it is an object of the present invention to provide a novel diffusion reactor free from the above problems.
It is a further object of the present invention to provide a novel diffusion reactor suitable for cleaning the same.
It is a still further object of the present invention to provide a novel diffusion reactor suitable for avoiding a cleaning chemical from over-etching the inner wall of a reaction chamber of the diffusion reactor.
It is yet a further object of the present invention to provide a novel diffusion reactor suitable for energy saving.
It is another object of the present invention to provide a novel method of cleaning a deposition on an inner wall of a reaction chamber of a diffusion reactor free from the above problems.
It is a further object of the present invention to provide a novel method of cleaning a deposition on an inner wall of a reaction chamber of a diffusion reactor without any over-etching to the inner wall of the reaction chamber by the cleaning chemical.
It is a still further object of the present invention to provide a novel method of cleaning a deposition on an inner wall of a reaction chamber of a diffusion reactor for realizing an energy saving.
The present invention provides a reaction chamber having jigs, top and bottom openings and a cleaning system. The cleaning system includes a cleaning solution supplier provided under the top opening for spraying a cleaning solution entirely within the reaction chamber to supply the cleaning solution on an inner wall of the reaction chamber and surfaces of the jigs, and a sloped bottom plate that closes the bottom opening so that the cleaning solution falls onto the sloped bottom plate and flows off of the sloped bottom plate.
The above and other objects, features and advantages of the present invention will be apparent from the following descriptions.